Fuel injector and check-valve

Abstract: An improved high-pressure fuel injector (10) and check-valve disks (20) therefore having annularly-spaced passages including holes (46). A preferred embodiment for EMD diesel and dual-fuel engines is a unit injector (10) with a flat circular valve disk (20) having a plurality of equally-spaced holes (46) located in a ring closely inwards of a ledge (34) of an associated valve cage (19) and closely outwards of a delivery opening (40) of an associated valve seat (39). Alternative disk and injector embodiments are disclosed in the specification.

Description: This invention relates to check-valves for use in high-pressure fuel injectors. It is known in the art relating to unit fuel injectors for diesel engines to provide a positive displacement plunger pump with a controlled output to pump fuel at high-pressure through a spray tip directly into an associated combustion chamber for combustion therein. A well-known feature of such injectors is the provision of a flat check-valve to prevent the back-flow of fuel or combustion gases from the combustion chamber and spray tip into the plunger pump location. A known type of flat check-valve is in the form of a small disk having the outer edges scalloped to provide flow passages for fuel when the valve is open and seated upon an annular seat open internally to a flow chamber. Such check-valves have been used for many years in some of the unit fuel injectors made by General Motors Corporation and subsequently by Diesel Technology Corporation, including those supplied for use in the well-known Electro-Motive Division (EMD) diesel and dual-fuel engines manufactured for railroad locomotives and other applications. US-A-4550875 discloses a check valve in accordance with the preamble of claim 1. A check valve in accordance with the present invention is characterised over US-A-4550875 by the features specified in the characterising portion of claim 1. The present invention provides improved embodiments and concepts for a disk check-valve for use in and in combination with high-pressure fuel injectors of the type described and equivalent applications. In a preferred embodiment, the injector is a unit type diesel fuel injector, particularly one for use in EMD diesel engines and the check-valve comprises a circular disk having flow passages comprising a plurality of holes equally spaced on a circle between the edge and the centre of the disk. At present, seven holes are preferred. Such an arrangement has been shown to apparently provide more stable action of the check-valve along with reduced pumping force required for injection at the higher fuel rates needed for recent engine applications. Improved combustion and operational efficiency have been obtained as a result. Numerous variations of the concept are contemplated as potentially providing similar advantages. These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings, in which: Figure 1 is a cross-sectional view of one type of unit fuel injector for EMD diesel engines and incorporating a check-valve disk according to the present invention; Figure 2 is an enlarged view of the area in circle 2 of Figure 1 showing a check-valve and spacer assembly; Figure 3 is an exploded pictorial view of the assembly of Figure 2; Figure 4 is a plan view of a valve disk according to a preferred embodiment of the invention; Figure 5 is a plan view showing a prior-art valve disk; and Figures 6-8 are plan views similar to Figure 4 and showing exemplary alternative embodiments of check-valve disks for use in high-pressure fuel injectors according to the broader aspects of the present invention. Referring now to the drawings in detail, numeral 10 generally indicates a fuel injector of the high-pressure unit direct-injection type and, in particular, one intended for use in engines manufactured by Electro-Motive Division (EMD)of General Motors Corporation. The illustrated injector is representative of many other high-pressure direct-injection fuel injectors for diesel fuel and other liquid and semi-liquid fuels which may make use of check-valves in accordance with the present invention. Injector 10 includes a body 11 and a thread-attached nut 12 within which are clamped a spray tip 14 carrying a needle-valve 15, a spring cage 16 carrying a valve spring 18, a check-valve cage 19 carrying a check-valve disk 20 according to the invention, a spacer 22 and a bushing 23 receiving a reciprocable plunger 24. Passages 26 in the body 11 and the bushing 23 supply fuel to the bushing interior for pumping under high-pressure by the plunger 24. A follower 27 engages the plunger 24 for actuating it mechanically in response to the engagement of a cam, not shown. Control of the amount and timing of the fuel injected each cycle is provided by mechanical rotation of the plunger 24 in the bushing 23 through a rack 28 and gear 30 which varies the effective length of the pumping stroke in known manner. If desired, known means for electronically controlling the fuel rate and timing could alternatively be used. As shown in Figures 2 and 3, the check-valve cage 19 has a flat upper surface 31 with a central recess 32 defining a delivery chamber 33 surrounded by an annular abutment in the form of a ledge 34 spaced slightly below the upper surface 31 and having an inner periphery 35 defining the outer edge of the delivery chamber. A cylindrical outer rim 36 borders the ledge 34 and joins it with the upper surface 31. Delivery passages 37 extend from the chamber 33 to connecting passages in the spring cage 16 and spray tip 14 leading to orifices in the form of spray holes 38 in the end of the spray tip 14 which are controlled by the needle valve 15. The spacer 22 includes a flat lower surface 39 which sealingly engages the upper surface 31 of the check-valve cage 19. A central delivery opening in the form of orifice 40 connects the delivery chamber 33 with a pumping chamber 42 formed within the bushing 23 and bounded by the plunger 24. The surface 39 also forms a valve seat surrounding the orifice 40. The check-valve disk 20 has opposite flat sides 43 which are identical with one another to avoid installation errors. It is preferably made of alloy steel and has adequate thickness to withstand the fuel pressures and seating forces exerted thereon, and to provide suitable mass for stable operation. An outer edge 44 is circular and seats upon the ledge 34 of the valve cage 19 with close clearance to the outer rim 36. A group of seven equally-spaced holes 46 through the disk 20 are centred on a circle 47 concentric with the edge 44 and centred on a central axis 48 of the disk. The holes are preferably all contained within in a band spaced (1) outwards of a circle 49 (Figure 4) of diameter equal to the diameter of the orifice 40 at the valve seat plus the radial clearance between the disk 20 and the outer rim 36 when the disk 20 is centred in the recess 32, and (2) inwards of the inner diameter of the ledge 34 that opens to the delivery chamber 33. The total area of the holes 46 is preferably in the range of 10-30 percent of the face area of the disk 20. The total area of the holes is sufficiently larger than that of the orifice 40 and passages 37 as not to significantly restrict fuel flow into the chamber 33. Preferably the total flow area of the holes 46 is about 1.5 times the flow area of the delivery orifice 40. In operation of the preferred embodiment of the invention, low-pressure fuel is admitted through the supply passages 26 to the pumping chamber 42 when the plunger 24 is raised. Rotation of a cam, not shown, against the follower 27 cyclically reciprocates the plunger down and up, pressurising and pumping a controlled amount of fuel from the chamber 42 during each downward stroke of the plunger. The volume of pumped fuel is controlled by the position of the rack 28 and gear 30 which rotate the plunger to mechanically control the timing and volume of the fuel discharged. In other embodiments electrical or other control means might be used for this purpose. The discharged fuel is passed at high pressure through the orifice 40 and flows radially outwards over the check-valve disk 20 as it is seated upon the ledge 34 of its cage 19 in a valve-open position. The fuel then passes through the holes 46 into the valve cage recess 32 and out through the three passages 37 and connecting passages in the spring cage 16 and spray tip 14 where the fuel pressure opens the needle-valve 15. The fuel is then atomised and delivered to the associated engine combustion chamber by passing through the spray holes 38 as is well-known in the art. Upon cut-off of the pumping action, the pumping chamber 42 is opened to the low-pressure fuel delivery passages 26 and the needle-valve closes, cutting off fuel delivery. Residual pressure in the delivery chamber 33 then forces the check-valve disk 20 upwards against the valve seat 39, closing the orifice 40 against the return flow of fuel and maintaining a barrier against the intrusion of combustion gases from the cylinder into the injector passages and the pumping chamber 42. Preferably, in a flat steel check-valve disk according to the present invention for use in EMD engine fuel injectors, the holes in the disk have diameters in the range of 1.27-1.778 mm (0.05-0.07 inches), and are equally spaced from one another on a circle of a diameter in the range of 5.08-7.62 mm (0.20-0.30 inches). The disk has a diameter in the range of 7.62-10.16 mm (0.30-0.40 inches), and has a thickness in the range of 1.016-1.524 mm (0.04-0.06 inches). In a preferred embodiment for use in injectors for EMD engines and best shown in Figure 4, the flat valve disk is made of alloy steel and has a thickness of about 1.27 mm (0.05 inches) and diameter of about 9.398 mm (0.37 inches). Seven holes of about 1.524 mm (0.06 inches) diameter are equally spaced from one another and are centred on a circle 47 of about 5.842 mm (0.23 inches) diameter. The disk is seated on a ledge 34 having an inner diameter 35 of about 7.366 mm (0.29 inches) and has a diametrical clearance averaging about 0.254 mm (0.01 inches) within the outer rim 36. The orifice 40 in the mating valve seat 39 is of about 3.302 mm (0.13 inches) diameter. These dimensions assure that a centred disk will have a radial sealing band of about 0.508 mm (0.02 inches) between the valve seat orifice 40 and the inner edges of the disk holes 46 when the valve is closed. This is also the approximate length of the minimum radial flow path for fuel travel across the face of the disk when the valve is open. It is considered that a short flow path is desirable for stable disk operation but this is about as small as the sealing band can be made to assure positive sealing within the limits of reasonable manufacturing tolerances. On their outer edges, the holes 46 are approximately aligned with the inner diameter of the ledge 34 on which the disk rests when the valve is open. Thus, essentially the full area of the disk holes 46 is available for fuel flow therethrough. Figure 5 illustrates a current check-valve disk 50 which has been successfully used in EMD engine injectors for many years. It is of similar material and has equivalent thickness and outer diameter dimensions to the preferred disk embodiment previously described. It differs in that instead of the seven holes of the first embodiment it has three arched cut-outs 51 which could also be called scallops or slots. These cut-outs extend from the outer edge 52 inwards sufficiently far as to provide adequate area for low-restriction fuel flow when the disk is seated on the ledge 34 of the previously-described injector valve cage 19. Nevertheless, at the maximum flow settings of recent high output fuel injectors, flow irregularities, called "knocking", were identified, which testing indicated might be due to unstable motion of the check-valve disk 50 during the pumping stroke, when the disk should remain seated on the ledge 34. It is conjectured that such action may have resulted from the rapid radial outflow of fuel over the upper side of the disc from the orifice 40 in the valve seat 39 to the inner edges of the cut-outs 51 causing momentary reductions in pressure above the disk sufficient to allow system pressure below the disk to lift it erratically from its seat on the ledge 34. The present invention avoids this erratic action by providing openings through the disc at locations which reduce the length of the radial flow path from the orifice 40 to the nearest openings for fuel flow. Tests showed that reduction of the path length from about 1.194 mm (0.047 inches) as found with the prior disc 50 to no more than 0.889 mm (0.035 inches) was effective to stabilise the disc with the current maximum flow rate. This might be done by merely adding openings to the present disk between the cut-outs or by replacing the cut-outs with a plurality of holes as in the preferred embodiment of the present invention. The latter is preferred as it further shortens the flow path and increases flow area for increased stability whilst reducing the stress levels to which the disk is subjected during operation of the injector. Alternative disk designs which are among those contemplated within the scope of the present invention are shown as examples in Figures 6-8 of the drawings. In Figure 6, a disc 54 is shown having a circular edge but only five holes 55 equally spaced from one another and each one of a size equal to those of the preferred embodiment. The five holes would still provide a flow area greater than that of the orifice 40. Alternatively fewer or more holes might be acceptable in particular cases. Figure 7 shows a disk 56 with eight equally-spaced radially-positioned oblong holes 58 therein, to increase flow area without increasing internal stresses in the disk. Figure 8 shows another embodiment of a disk 59 where three smaller holes 60 are added to legs 62 formed between the cut-outs 51 of the previous disk 50. Whilst the invention has been described by reference to certain preferred embodiments thereof, it should be understood that numerous changes could be made within the scope of the present invention. Accordingly it is intended that the scope of the present invention should not be limited solely to the disclosed embodiments, but that it should have the full scope permitted by the language of the following claims.

Claims: A check-valve for use in a high-pressure unit fuel injector (10) having a member (22) with a central fuel delivery opening (40) to be intermittently supplied with high-pressure fuel and a flat valve seat (39) surrounding the opening (40), a valve cage (19) seated against the member (22) and including a recess (32) adjacent the valve seat (39), the recess (32) including an annular ledge (34) facing the valve seat (39), the ledge (34) being centred on and having an inner periphery (35) substantially larger than the delivery opening (40), an inwardly-facing annular rim (36) surrounding the ledge (34), and a delivery chamber (33) inward of the ledge (34) for receiving fuel delivered from the delivery opening (40), wherein said check-valve comprises a disk (20;54;56;59) receivable in the recess (32) and having opposite first and second flat faces (43) alternately seatable against the valve seat (39) and the ledge (34) respectively, an outer edge (44) receivable in opposed relation to the rim (36) and having limited radial clearance therefrom when centred in the recess (32), characterised by a plurality of holes (46;55;58;60) extending through the disk (20) between the flat faces (43), the holes (46;55;58;60) being located wholly outwardly of a circle of diameter equal to the sum of the diameter of the delivery opening (40) at the valve seat (39) and the radial clearance of the centred disk (20), said holes (46;55;58;60) forming at least a portion of the total flow area of flow passages extending between the opposite faces (43) of the disk (20) within a diameter equal to that of the diameter of an inner periphery (35) of the ledge (34). A check-valve according to claim 1, in which said flow passages consist only of said holes (46;55;58) in said disk (20;54;56). A check-valve according to claim 2, in which said holes (46;55;58) are angularly equally spaced from one another. A check-valve according to claim 3, in which there are at least five and not more than 9 holes (44;55;58). A check-valve according to claim 4, in which there are exactly 7 holes (44). A check-valve according to any one of the preceding claims 2 to 5, in which the total flow area of said holes (46;55;58) is about 1.5 times the flow area of the delivery opening (40). A check-valve (20;54;56;59) according to claim 1, in which the holes (46;55;58;60) are of equal size and are equally spaced from one another on a circular axis (47) located intermediate the centre (48) and the edge (44) of the disk (20;54;56;59). A check-valve (20;54;56;59) according to claim 7, in which the total area of the holes (46;55;58;60) is in the range of 10-30 percent of the face area of the disk (20;54;56;59). A check-valve (20;54;56) according to any one of claims 1 to 8, in which the check-valve disk (20;54;56) is made of steel material. A check-valve according to any one of claims 1 to 9, wherein the holes (46;55;58) have diameters in the range of 1.27-1.778 mm (0.05-0.07 inches), the circle has a diameter in the range of 5.08-7.62 mm (0.20-0.30 inches) and the disk has a diameter in the range of 7.62-10.16 mm (0.30-0.40 inches) and a thickness in the range of 1.016-1.524 mm (0.04-0.06 inches). A check-valve according to claim 10, in which there are exactly 7 holes (46) having diameters of about 1.27 mm (0.06 inches), the circle (47) has a diameter of about 5.842 mm (0.23 inches), and the disk (20) has a diameter of about 9.398 mm (0.37 inches) and a thickness of about 1.27 mm (0.05 inches). A check-valve according to claim 1, in which said flow passages also include cut-outs (51) extending from the disk edge inwards of a circle equal to the inner periphery (35) of the ledge (34). A check-valve according to claim 12, in which said holes (60) are located angularly between the cut-outs (51). A check-valve according to claim 12, in which there are at least three equally-spaced cut-outs (51). A check-valve according to claim 14, in which the cut-outs (51) form equally-spaced legs (62) extending to the edge of the disk (59) and the holes (60) are in the legs (62).

Inventors: BORMANN RODNEY JOEL, GOETZKE MICHAEL BARRY, TUPEK RICHARD WAYNE, BORMANN, RODNEY JOEL, GOETZKE, MICHAEL BARRY, TUPEK, RICHARD WAYNE
Applicants: GEN MOTORS CORP, GENERAL MOTORS CORPORATION
Application year: 1994
Main classification: F02M59
IPC codes: F02M59, F02B3, F02M57